1) Field of the Invention
Embodiments of the invention relate to communications networks and systems, as well as a method therefor.
2) Description of the Related Art
A communication system can be seen as a facility that enables communication sessions between two or more entities. The communications may comprise, for example, communication of voice, electronic mail (email), text message, multimedia, other data and so on. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication network may be a local network.
A user can access a communication system by means of an appropriate communication device. A communication device of a user is often referred to as user equipment (UE). A communication device is provided with an appropriate signal receiving and transmitting apparatus for enabling communications, for example enabling fixed or wireless access to a communication network or communications directly with other users. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. A user who has accessed a system may also be provided broadcast or multicast content. Non-limiting examples of the content include downloads, television and radio programs, videos, advertisements, various alerts and other information.
Embodiments of the invention have particular but not exclusive application to local area (e.g. autonomous) cellular communications systems. In such systems, an arrangement of base stations in a communication system such as a cellular communication system, also referred alternatively as Node B's or evolved NodeBs (eNBs), operate generally without central control whereas conventional systems generally include a network controller for example. This enables cheap uncoordinated deployment of Node Bs in local area environments.
An autonomous component carrier selection scheme for LTE-A (Long Term Evolution Advanced) radio systems has been proposed which relies on each cell automatically selecting one of the component carriers as its primary carrier (also some-times called the base carrier). The primary/base carrier is assumed to be used for initial connection of User Equipment e.g. terminals in the cell. Depending on the offered traffic in a cell and the mutual interference coupling with the surrounding cells, transmission/reception on all component carriers may not always be the best solution. It has therefore been proposed that each cell dynamically selects additional component carriers for transmission/reception as well. The latter is referred to as selection of secondary component carriers (also some-times called extended carriers). All component carriers not selected for primary or secondary are completely muted (uplink/downlink) and not used by the cell.
The paper 3GPP TSG RAN WG1 No. 55-bis Meeting, Ljubljana, Slovenia, Jan. 12-16, 2009, entitled “Use of Background Interference Matrix for Autonomous Component Carrier Selection for LTE-Advanced” describes a system where eNBs in an autonomous network maintain information relating to interference coupling with surrounding cells by means of Background Interference Matrices (BIMs). A BIM is built up locally by each eNB based on measurements from the terminals (e.g. user equipment which) served by the eNB. Depending on the BIM and e.g. the offered traffic per cell, each eNB will autonomously select the component carriers it needs, while at the same time ensuring that it does not create excessive interference in the surrounding eNBs. Thus, the autonomous component carrier selection scheme essentially provides an automatic mechanism for dynamic frequency re-use on a component carrier resolution for LTE-Advanced based on BIM, and other information. The autonomous component carrier selection scheme has been mainly proposed for LTE-Advanced for optimizing the system performance in local area environments, where there is dense deployment of low power eNBs such as micro cells, Pico cells, Home eNBs, etc
In communication systems such as for example autonomous (local area environments) systems which use with low power eNBs, such eNBs are typically not constantly on. Some low power eNBs are switched on and off depending on various needs; this is especially the case for Home eNBs owned by individual persons. Such Home eNBs are typically only switched on when the owner needs wireless access, whilst otherwise it is off, or in some kind of sleep/hibernation mode. Thus the number of active eNBs in a local environment becomes time-variant. In known systems, parameters are stored by eNBs relating to mutual interference coupling between eNBs, typically as Background Interference Matrix (BIM) data. As the dimensions of the BIM that each local eNB maintains depends on the number of neighbouring eNBs (that are on), the BIM information also needs updating when existing eNBs are switched off (or goes into sleep mode), or when other eNBs are switched on.
Secondly, as the local BIM information at each eNB is based on measurements from its associated terminals (including measurements to the new eNB); it takes time to build new BIM information whenever a new eNB is switched on.
It is an object of embodiments of the invention to provide an improved system which allows more efficient maintenance where eNBs are switched on and off over time.